Molecular storage of information



July 5, 1960 R. H. DlcKE MOLECULAR STORAGE OF INFORMATION Filed March 12, 1956 WH VfGH/DE 5 TORHGE CELL /EEC''ZZ PULSE' /IPECHZL PU .5E

F 4 INVEN TOR.

HUBERT H. 7A/:KE-

BY rmz/Vfy iatented July s, 1960 fThis invention relates to molecular or atomic memory systems and it has for its object to provide a novel and improved method and means for storing information in the form of microwave energy.

4Another object of the invention is to provide a novel and improved system `employing a microwave resonance to store information in a series of pulses, and for recalling such information after a desired delay time by the application of a recall pulse.

Another object is to provide a molecular or atomic memory system employing a microwave resonant gas to store information in the form of microwave pulses at the 4resonance frequency of said gas.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

'The various objects of the present invention are achieved by utilizing a molecular microwave system in which a microwave resonance phenomenon is employed to store information in the form of a series of pulses. The function is similar to that of a delay line except that the storage time (Le. delay time) is variable, since the infomation is read out by applying a recall pulse to the device.

In carrying out the invention, the atoms or molecules of the particular microwave resonance medium or gas employed f or storage purposes, such as ammonia, are contained in a long waveguide type cell or chamber excited in a mode for which the microwave travels as a plane wave down the cell. The atoms or molecules in the cell are initially in a condition of thermal equilibrium. information is fed into the gas in a series of weak pulses at the resonance frequency of the gas. Thereafter, on feeding in a recollection pulse as hereinafter described, the gas proceeds to radiate the information previously stored.

`In one embodiment of the invention the stored information is recalled by one or more recollection pulses, i.e. a microwave pulse of such strength that the atoms or molecules are exoitedfrom one of the two energy states" of the gas to the other; Upon feeding in one recollection pulse, the gas radiates the information as a series pulse which serves Vas a recall pulse, causing the gas to radiate back the stored information.

The invention is described more in detail in connection with the accompanying drawing, in which:

Fig. 1 is a schematic diagram, partly in block form, of a molecular or atomic memory system embodying the invention;

fFig. 2 is a diagrammatic perspective view of a waveguide type storage cell for use in the system of Fig. l;

Figs. 3a and 3b are diagrams used in describing the operation of the system pursuant to one embodiment of of pulses in the reverse order, but by employing a double time separated pulse the recalled memory pulses may be `made to come out inthe same order as they went in. In another embodiment of theinvention the gas is rst prepared for the reception of information pulses by the application of a preliminary pulse which initiates the infomation input period. This preliminary pulse is a pulse of such strength that the individual molecules are thrown from a state of definite energy into a superposition state in which they are partly and with equal probability in each of two energy states defining the resonance frequency. The preliminary pulse is followed by a series of Weak information pulses, and by a storage interval during which the gas is not excited. The storage interval liS followed, by another pulse similar to the preliminary,

` pipe waveguide 3. The structure of the cell 2 will be described later with particular reference to Fig. 2. rThe output end of the cell 2 is coupled to a further waveguide section 4. The cell 2 is made gas-tight by a pair of microwave permeable windows 5 and 6 formed of a material such as quartz or mica. One of said windows 5 is positioned in the waveguide section 3 near the input end of cell 2 while the other window 6 is positioned in waveguide section 4 nea-r the output end. of cell 2. A source "i of recollection pulses is coupled to the waveguide section 3 via another section of absorptively terminated rectangular waveguide 8 and atdirectional coupler 9.

The cell 2 contains a gas at low pressure capable of exhibiting molecular resonance. The gasnormally-presents positive attenuation to microwave energy and se-L lectively absorbs microwave energy hat ;freguencies ,at` which the gas is resonant. Such gases are numerous ,and-

include, by way of example, ammonia, carbonyl sulde, and the methyl bolides. In :the present instance it `is as-: sumed that the chosen microwave resonant `gas` ismain-` monia the pressure of which is made lo-w enough so `that the molecules are thermally relaxed by wall collision. Y

Fig. 2 shows a waveguide `cell or chamber-2 whichy may be employed in the system of Fig. l. Thesaid cell;

comprises a long section of rectangular hollowpipe wave-.

guide having dielectric slabsll Iand 12 each of which isV in contact with one narrow sidewall ofthe cell anden-` tends along its longitudinal axis, toslow they/ave down to `g=?\, for which the wave is a planewave.

The cell 2 contains a series` of septa ,13,4 whichmay; comprise a plurality `of V.fine wires such ast 'tungsten mounted on suitable metallicsupports or frames 14, exa tending along the longitudinaltaxis4 of the cell..l A` convenient method of mountingis to seat the metallic` sides,

of the septa frames 14 in longitudinal 'slots 15 in the-dil electric slabs 11 and 12, asillustratedin Fig. r*Ehesepta 13` are electrically` charged,` `as by a sourceoftpotential 16 through-potentiometer 17, to a series of` potentials to detune the gas molecules in the1 cell.. fr

In the operation of the system describedabove ithe memory time is given by the time` required `for the molecules to reach walls inthe cell 2. With :a large wavestorage capacity will be obtainable.` Assuming a-.band width of l0 mc., information `can be fed into the cell 42` at the rate of l0 pulses/,aseo and` each pulsetcan have'` If the band is made wider, theY a variety of strengths.

pulse rate can be higher lbut the signal is`weaker` Y 3 vInfomation from the source i is fed into the gas in cell 2 in a series of weak pulses at the resonance frequency of the gas. In the diagram of Fig. 3 these pulses are represented as A, B, C and D.` After the information Vpulses are fed in, a-recollection pulse from source 7 is fed in, the recollection pulse being a `microwave pulse of such a strength as to excite the gas atoms or molecules from-one (the lower) of the two energy states which define the resonance frequency of the gas to the other (the higher) energy state.` The gas then proceeds to radiate the information as a series of pulses in the reverse orderUD, C, E, A, as indicated in Fig. 3. However, by employing a double time-separated recollection pulseas indicated in Fig. 3, the memory pulses are made to come out in the same order in which they went in.

Another different mode` of operation will now bedescribed with reference to Fig. 4. The gas is rst prepared for the reception of information pulses by a pulse S which initiates the information input period. The pulse S is apulse of such strength that the molecule is thrown from a state of definite energy intoA a superposition state in Iwhich it is partly and with equal probability in each of two energy states. This initial pulse is followed by a series of weak'information pulses such as A, B, C in Fig. 4, .whose spacing and/or strength and phase Yis a source of information. The information input interval is followed by a storage interval during which the gas is not excited. This is in turn followed by another pulse R (like the pulse S) which serves as a recall pulse after which the gas radiates back the information stored.Y

The theoryof operation is believed to be as follows: the molecules may be divided into classes of different resonance frequencies because of the doppler effect and/or perturbing static elds. The initial pulse S puts allmolecules in Ia superposition energy state such that the probability of iinding a molecule in the upper energy state equals the probability of finding it in the lower energy state. The subsequent rtrain of information pulses A, B, C selectively excites molecules of a given class (ie. those of a given definite resonance frequency) by an amount proportional to the amplitude of the cosine transform of the corresponding frequency. (Here the time origin is taken as the time of the first pulse S.) The probability of being in the upper energy state may be increased or decreased depending on the sine of this Fourier component.

After the initial pulse S followed by the train of inform-ation pulses, the cosine spectnal distribution of the information pulse is written into the gas as a distribution in internal temperature over the classes of various resonance frequencies. The information as to the sine transform is carried in the changes in internal phases of the atoms. Remarkably enough it is possible to completely destroy these phases by making them random after the information pulses have been applied to the gas without any real loss in vinformationV stored. The information is completely contained in either the cosine transform or the sine transform. The reson for this is that the information is all containedin a time interval t 0,`measuring time t after the initial pulse S, and the sine and cosine transforms are directly connected. Consequently, there is nonecessity for carefully controlling static elds to accurately preserve interval molecular phases. The internal temperature is independent of such fields. This allows a longer storage time and it may be possibleto get storage times in excess of 100 usec.

The effect of the second (recall) pulse R may be described as follows: because of thedistributionin internal temperature as a function of resonance frequency of the gas, the absorption eflicient of the gas is a complex function of frequency. Thus, because of the Kramers- Kronig relation between real and imaginary parts of the dielectric constant, the dispersion properties of the gas are uniquely given by the absorption spectrum. The' Kramers-Kronig relation is set forth at page 343 of 4 i Microwave Spectroscopy by Townes and Schawlaw (Mc- Graw-Hill, 1955). If the gas is excited by a pulse it continues to radiate afterward because of the frequency dependence of Ithe dielectric constant of the gas. This is just such as to cause the gas to radiate back the informa- Y states are not required and 'theconditions on uniformity of static fields is much less severe.

What is claimed is:

1. Vinformation storage apparatus comprising a gas chamber, a microwave resonant gaseous medium confined within said chamber, the gas molecules of said medium having electric dipole moments 'and being'consources to said chamber, and means for applying saidV revertible by microwave energy from a microwaveattenum,

tive state to a microwave radiant state, a source of microwave pulses, containing the information to be stored, said pulses being of a frequency which is a resonant frequency of said medium for impressing said information on said medium in its attenuative state, a source of vre;V

collection pulses of microwave energy at a resonant'fre-l quency of said medium for inducingy the occurrence of energy level transitions between energy levels of said medium thereby converting said medium from said attenuative state to said radiant state, coupling means connecting both of said sources` to said chamber, and means for applying said recollection pulses to said medium at theV conclusion of the desired storage time intervalY to recall said stored information.

2. Information storage apparatus of the molecular type, comprising an elongated hollow waveguide having microwave transparent windows disposed at opposite ends thereof for defining a gas-tight chamber, a microwave resonant gaseous medium. confined within said chamber, the gas molecules of said medium having electric dipole moments and being convertible by microwave energy from a microwave iattenuative state to a microwave radiant state, a source of microwave pulses containing the information to be stored, said pulses being of a frequency which is a resonant frequency of said medium for impressing said information on said medium in its attenuative state, a source of recollection pulses of micro-= wave energy at a resonant frequency of said medium for inducing the occurrence of energy level transitions between energy levels of said medium thereby converting said medium from said attenuative state to said radiant state, coupling means connecting both of said collection pulses to said medium at the conclusion :of the desired storage time interval to recall said stored information. v

3. Apparatus according to claim 2, further comprising loading means extending longitudinally along opposite sides of said chamber foi-*imparting a plane wavefront to microwaves traveling tlierealong..

4. Apparatus according to claim 2, further comprising a series of septa extending longitudinally of` said chamber, and circuit means for applying successively increasing unidirectional electrostatic potentials to each successive one of said septa for detuning the molecules of said medium.

5. Apparatus according to claim 1 wherein one of said recollection pulses has a duration suicient to invert the molecular population of said medium between higher and lower energy levels.

6` Apparatus according to claim 5 includingmeans` for applying to said medium a second recollection pulse for inverting the order of radiation of recalled radiation pulses of said stored information, said second recollection pulse being spaced from the rst recollection pulse by aV time interval at least as long as the time interval required for the application of said information pulses to said medium.

7. Apparatus according to claim 1 wherein said attenuative state is a state of thermal equilibrium and including means for applying to said medium, preceding the application of said information pulses, a preliminary conditioning pulse to cause the individual molecules of said medium to assume said two energy levels simultaneously 'with equal probability of being in either level.

References Cited in the file of this patent UNITED STATES PATENTS 2,718,629 Anderson Sept. 20, 1955 2,745,014 Norton May 8, 1956 2,749,443 Dicke et al. June 5, 1956 

